In recent years, it has been strongly desired to restrain global warming. Under such a circumstance, power plants have been desired to restrain the generation of CO2, SOX, NOX, etc. by reducing the consumption of fuel for generating power while improving power generation efficiency.
In thermal power plants using steam turbines, gas turbines, etc., the temperature at the inlet of the turbine has been increased, as an effective technique for improving efficiency.
The turbine has stationary parts and rotational parts such as a rotor and rotor blades, and it is essential to provide a gap between the stationary parts and the rotational parts to avoid the contact therebetween.
Therefore, working fluid inevitably leaks through the gap outside the turbine blades, and metal surface is exposed to the temperature of the working fluid. Therefore, when high-temperature working fluid is used, even heat-resistant alloy may be unable to meet required strength characteristics.
Accordingly, a structure for cooling partially according to need has been proposed. For example, there is one conventional structure in which working fluid reduced in temperature by the complete of the work in a turbine stage on the downstream side is partially guided, to the outer surface of the turbine rotor or to the outer circumferential wall of the leading edges of the rotor blades in a stage on the upper stream side to cool the working fluid, and the cooled working fluid is emitted from the ground. It is assumed that this structure can be safely applied to a steam turbine having a main flow temperature of about 600° C. However, when this structure is applied to a gas turbine etc. having a main flow gas temperature of higher than 1000° C., sufficient cooling cannot be achieved since high temperature is kept also in the turbine stages on the downstream side. Further, since working fluid extracted from the middle stage is used for cooling and then emitted from the ground, the emitted working fluid cannot be recovered as power, which inevitably leads to reduction in efficiency.
Further, in Patent Document 2 for example, a space is formed between the outer surface of a pathway contacted with the main flow and the outer surface retaining blades, and an implant unit of the rotor blade has a conduction part. In this structure, space of on the upper stream side of the rotor blades and space on the downstream are communicated, and cooling medium passes therethrough for cooling. In such a communication structure, the temperature of the cooling medium is increased as approaching the downstream side of the cooling space, which clearly leads to reduction in cooling efficiency. When working fluid of the main flow does not have high temperature, there will be no particular problem since the increase in temperature of the cooling medium is not great. However, when high-temperature working fluid is used, it is difficult to achieve sufficient cooling.
As stated above, when working fluid of the main flow has high temperature, it is difficult to obtain sufficient cooling effect by the conventional techniques. Accordingly, cooling has been performed by increasing the amount of cooling medium. However, if the amount of cooling medium to be used is increased, efficiency of the entire plant is reduced, which is an obstruction to increasing temperature to improve power generation efficiency.